1. Field of the Invention
The present invention relates to a projector and a control method for the projector and, in particular, to shifting the position of a projected image and adjusting the luminance of black.
2. Description of the Related Art
Video image projection using a plurality of projectors has been conventionally performed to increase an information amount and/or brightness in a projected video image. To increase an information amount, for example, a method called multi-projection (or tiling) has been employed in which video images projected by a plurality of projectors are arranged next to one another to form a single large screen.
In such multi-projection, it is hard to arrange the projectors such that the video images projected by adjacent projectors do not overlap with each other at all, and thus, in some cases, adjacent video images are projected to partially overlap with each other. In this case, by adjusting display positions of the video images projected by the respective projectors to project identical video images in an overlapping portion, seams are made less noticeable.
However, when the video images are projected to partially overlap with each other, brightness in a region where the projected video images overlap with each other (hereinafter, referred to as an overlapping region) becomes higher than that in a region where the projected images do not overlap (hereinafter, referred to as a non-overlapping region) even if the identical video images are projected in the overlapping region. This hinders proper viewing. Hereinafter, a bright portion produced in an overlapping region in the aforementioned state will be referred to as a misadjusted black floating pattern.
Accordingly, Japanese Patent Application Laid-Open No. 2005-275077 discusses a multi-projection display device including a plurality of projector units that makes an adjustment to add (increase) luminance in a non-overlapping region, using an auxiliary illumination device.
In addition, there has been also known a projector that includes an image processing function to make an adjustment to add the luminance of black in a non-overlapping region.
Meanwhile, as discussed in U.S. Pat. No. 7,237,903, there is a technique to allow the position of a video image projected on a screen to be adjusted by changing the timing of superimposition of a video signal with respect to vertical and horizontal display periods of a display device.
FIG. 7A illustrates an overall projected video image after an adjustment is made to add the luminance of black in a non-overlapping region. FIG. 7B illustrates an overall video image projected when the positions of the video images projected by the individual projectors are shifted, by an image processing function, from the state illustrated in FIG. 7A to the right on the drawing surface of FIG. 7A.
As illustrated in FIG. 7B, the luminance of black in the projected video image becomes uneven if the positions of the projected video images are adjusted by the method discussed in U.S. Pat. No. 7,237,903 after the processing to adjust the luminance of black is carried out by the image processing function to suppress generation of a misadjusted black floating pattern.